A THESIS SUBMITTED TO THE DEPARTMENT OF HORTICULTURE, COLLEGE OF AGRICULTURAL SCIENCES, SCHOOL OF GRADUATE STUDIES, ARBA MINCH UNIVERSITY

Abstract

Sweet potato (Ipomoea batatas (L.) Lam.) is one of the most economically important food security and cash crop cultivated in Ethiopia. Low soil fertility and crop nutrient imbalances are limiting Ethiopian producers from realizing the potential yield of the crop. Particularly, demand for orange-fleshed sweet potato (OFSP) is increasing due to their nutritional importance of reducing vitamin A deficiency; yet its production and productivity are low partly due to knowledge gaps in selection of adaptable and high yielding varieties to specific agro ecologies. Thus, the field experiment was conducted with the objective of evaluating the effect of blended NPSB fertilizer rates on OFSP varieties in two different agro-ecological zones of Wolaita and Gamo during 2022 cropping season for five mon ths. The treatment consisted of three recently released OFSP varieties (Alamura, Dilla, and Kabode) and four rates of NPSB (0, 79.5,159, and 238.5 kg ha-1 ). The experiment was laid out in a 3x4 factorial combination arranged in a Randomized Complete Block Design (RCBD) with three replications. Data were recorded on phenology, growth, root yield, and yield components analyzed using SAS 9.2. The analysis of variance revealed that Variety Kabode matured earlier (132 days after planting) and when fertilized with 238.5 kg ha- 1 NPSB resulted in the highest root diameter (6.60 cm) at Arba Minch. Also, the highest root weight (500.58 g/root), and marketable root yield (49.84 t ha-1 ) were recorded at the same NPSB rate and same location. Variety Dilla, treated with 159 kg ha - 1 resulted in the highest root dry matter (95.10%) at Arba Minch site. Marketable root yield significantly and positive correlated with root diameter (r=0.59), root weight (r= 0.56), and harvest index (r=0.56). At Areka site, variety Kabode with NPSB rate of 79.5 kg ha 1 produced 288.67 agronomic efficiency (AE). However, at Arba Minch site, the highest AE (174.71) was obtained from the same variety, but treated with 159 kg ha-1 NPSB. Nevertheless, variety Kabode treated with 238.5 kg ha-1 gave the highest net benefit (342,856.6 ETB ha-1 ) at Arba Minch, while at Areka, the highest net benefit (328,138.4 ETB ha-1 ) was obtained from the same variety treated with 159 kg ha-1 NPSB. Hence, variety Kabode with 79.5 kg ha-1 NPSB and 159 kg ha-1 NPSB at Areka and Arba Minch sites respectively were the best combinations and recommended for sweet potato producers